Cancer drug discovery has traditionally focused on targeting DNA synthesis and cell division, resulting in drugs such as antimetabolites and DNA alkylating agents. Although these drugs show efficacy, their lack of selectivity for tumor cells over normal cells can lead to severe side effects. The recent recognition that certain genes are associated with cancer has resulted in several rational and targeted drugs for cancer therapy. However, many of the available targeted cancer treatments inhibit only a specific aspect of cancer progression such as proliferation, angiogenesis or metastasis. This limits their utility and necessitates their use in combination with traditional chemotherapeutic agents. Examples of such targeted cancer drugs include erlotinib (Tarceva®) and bevacizumab (Avastin®). Erlotinib inhibits cell proliferation, while bevacizumab is an anti-angiogenesis drug. These drugs target kinases or proteins involved in kinase signaling pathways. Recent findings indicate that matriptase, a transmembrane serine protease, plays a role in triggering the formation of tumor cells. Unlike kinases, the localization of matriptase on the cell surface makes it more accessible to a potential inhibitor. Matriptase is over-expressed (up to several hundredfold) in all phases of cancer in multiple cancer types and has also been shown to play a role in invasion and metastasis. Therefore, a matriptase inhibitor could comprise a potential first-in-class drug with a broad spectrum of anti-tumor activity including anti-proliferative and anti-invasive activities.
Matriptase is a multi-domain 80-kDa type II transmembrane serine protease and belongs to the S1 trypsin-like family. Matriptase is involved in matrix remodeling/degradation, regulation of cell growth and survival, cell motility, cell morphogenesis, and activation of other membrane bound proteins. It is also called the membrane-type serine protease-1 (MT-SP1), the tumor-associated differentially expressed gene-15 (TAGD-15), or epithin in mouse. Matriptase is overexpressed in a vast array of human tumors of epithelial origin including prostate, ovarian, uterine, colon, epithelial-type mesothelioma, cervical and head and neck squamous cell carcinoma. Epidemiological studies have revealed that increased expression of matriptase relative to HAI-1 correlates with the grade of the tumor and results in poor prognosis in breast and ovarian cancer.
The role of matriptase has been well established in pathways involved in cancer even though the exact function of human matriptase has not been elucidated. Matriptase enhances tumor cell proliferation through phosphatidylinositol 3-Kinase signaling and invasion through the HGF/cMet and uPAR activation. Glycosylation of matriptase by UDP-GlcNAc alpha-mannoside beta1-6-N-acetylglucosaminyltransferase (GnT-V) plays a key role in metastasis by increasing the stability of degradation-resistant active form of the enzyme. Furthermore, matriptase activates other proteases such as receptor-bound urokinase-type plasminogen activator (uPA). Overexpression of uPA or its receptor (uPAR) is a feature of malignancy and plays a critical role in angiogenesis, tumor invasion and metastasis. Down-regulation of matriptase inhibits tumor invasion through suppression of uPAR activation.
Several other “trypsin like serine proteases” such as uPA, trypsin, plasmin, hepsin and kallikrein play a critical role in cancer affecting various pathways leading to angiogenesis, invasion and metastasis. Urokinase-type plasminogen activator (uPA) plays a major role in extracellular proteolytic events associated with tumor cell growth, migration and angiogenesis. Many cancer cells secrete pro-uPA and its receptor uPAR. Binding of pro-uPA to uPAR leads to its activation, with subsequent generation of plasmin by the uPA-catalyzed hydrolysis of extracellular plasminogen. The increased production of plasmin leads to degradation of extracellular matrix both by plasmin itself and by other proteases that are activated by plasmin. The surface location of bound uPA provides directionality to the degradation of matrix, thereby assisting the directional migration of cancer cells. uPA in complex with uPAR also affects other biological processes including signaling pathways that influence cell proliferation. Hepsin is another type II transmembrane serine protease (TTSP) expressed on the surface of epithelial cells. It has been implicated in ovarian cancer and prostate cancer, where several gene expression studies have identified it as one of the most highly induced genes. Hepsin over-expression was associated with basement membrane disruption and was shown to be connected the HGF/c-Met pathway and uPA pathway connecting hepsin to the pathways leading to basement membrane disruption and tumor progression.
Therefore, inhibitors of matriptase and other related serine proteases could be of significant therapeutic value because of the following reasons:                potential to be used as a ‘mono-therapy’ due to wide expression and activity of matriptase and other proteases in both early and late stages of cancer        superior safety profile due to localization of matriptase, uPA and hepsin at the cell membrane which avoids the need of cellular entry of the drug        superior efficacy profile due to tumor-specific expression        potential for reducing morbidity due to a larger therapeutic window that results from fewer therapy-related side effects typically associated with cytotoxic agents        
Matriptase inhibitors have been described earlier e.g. in Enyedy, I. et al., J. Med. Chem., 2001, 44, 1349-1355; and in international patent publications WO 01/97794, WO 2004/058688, WO 2004/101507, WO 2008/085608, WO 2008/107176, WO 2008/097673, WO 2008097676 and WO 2008/107176. Other benzamidine compounds have been described earlier e.g. in Phillips, G. et al., J. Med. Chem., 1999, 42, 1749-1756; Phillips, G. et al., J. Med. Chem., 1998, 41, 3557-3562; and EP 0 813 525.